The goal of this project is to understand how populations of neurons in visual cortex integrate diverse types of information provided by synaptic inputs, including eye movement signals and attentional modulation. Much of our understanding of the visual system has been shaped by extracellular recordings from individual neurons In a single visual area. However, in the case of many diseases of the brain (such as amblyopia) and damage to the brain (such as that caused by concussive head trauma) impairment of functioning can not be understood in terms of a deficit in a single, focal region. Furthermore, an understanding of a complex process like visual attention or visual motor function cannot be obtained from recordings of single neurons in a single cortical area. In this project, we will utilize multi-electrode recording technology in one cortical area combined with stimulating and recording In another cortical area to determine how populations of neurons interact within and between brain regions. Specifically, the proposed experiments will employ chronically implanted 100-electrode arrays In macaque visual area V4 In conjunction with stimulation and recording from single electrodes in the frontal eye fields (FEF). Area V4 Is an idea! choice to explore questions of integration because of Its place in the visual hierarchy. It receives input from early visual cortex as well as higher level regions, including FEF. We will begin by measuring the correlation structure within a population of V4 neurons during visual stimulation in order to determine how it differs from the known structure of correlation in primary visual cortex. Once this is complete, we will record simultaneously in FEF and V4 to determine the types of neurons that are connected between these areas, and test the hypothesis that the FEF to V4 pathway plays a role in attentional modulation. Finally, we will stimulate in FEF and record populations of neurons in V4. We expect that FEF input will serve to synchronize groups of V4 neurons, enabling them to provide a more effective input to downstream cortical areas. These experiments will provide crucial insight into how the visual cortex integrates over small regions of space using information about eye movements and attentional modulation to produce behaviorally relevant output.